Embodiments of the disclosure relate generally to switching amplifiers, and more particularly to a gradient driver that is compatible with magnetic resonance imaging (MRI) systems.
In a MRI system, gradient drivers are configured to excite gradient coils located around an object, for example a patient, to generate magnetic field gradients along X-axes direction, Y-axes direction, and Z-axes direction. Typically, the gradient driver is a switching power supply which is composed of power semiconductor devices, such as insulated gate bipolar transistors (IGBTs), power metal oxide semiconductor filed effect transistor (MOSFET), etc. In order to control an electrical power that can be transferred by the gradient driver, the power semiconductor devices are usually operated in a pulse width modulation (PWM) method.
However, the PWM method will lead to a fast voltage (dv/dt) or current (di/dt) transient which could generate a lot of high frequency harmonic contents. As mentioned above, the high frequency harmonic contents may contaminate radio frequency (RF) signals that will be sensed by RF coils, and lead to a significant degradation of the MR image quality. The high frequency harmonic contents could be defined as differential mode (DM) electromagnetic noise and common mode (CM) electromagnetic noise. Usually, the magnitude of the CM electromagnetic noise is greater than the magnitude of the DM electromagnetic noise.
Therefore, it is desired to decrease the CM electromagnetic noise generated by the gradient driver.